The work on membrane receptors on human platelets and human polymorphonuclear leukocytes will continue. The receptor for endotoxin will be compared with the receptor of IgG Fc fragment. The analysis of conditions under which the Staphylococcal Protein A - IgG complex interacts with IgG Fc receptor will be conducted. The changes in the membrane of human platelets and human PMN leukocytes triggering clot-promoting activity of these cells will be studied. A new approach employing fluorescent probes will be applied. Analysis of human fibrinogen interaction with staphylococci will be conducted. The staphylococci-binding sites on normal and abnormal human fibrinogens will be further characterized. Their relation to the antigenic determinants of human fibrinogen will be studied. The work on immunoassay of human Platelet Factor 4 (PF4 Antiheparin Factor) will focus on setting up optimal conditions under which PF4 can be measured after release in vitro and in vivo. BIBLIOGRAPHIC REFERENCES: Hawiger, J., Hawiger, A., and Timmons, S.: Endotoxin-sensitive membrane component of human platelets. Nature (Lond) 256: 125, 1975; Des Prez, R.M., Bryan, C.S., Hawiger, J., and Colley, D.G.: The function of the classical and alternate pathways of human complement in serum treated with ethyleneglycol-tetraacetic acid and MgCl2-ethylene-glycol-tetraacetic acid. Infection and Immunity 11: 1235-1243, 1975.